1. Field of the Invention
The invention is directed to a stop fixture for use on overhead doors of the lift type which operate in side tracks by means of rollers and cable supported for movement from a vertical operative position to a horizontal overhead position.
2. Description of the Prior Art
Heretofore, door safety stops have been provided to prevent doors from falling in the event of failure of some supporting structure, particularly cables which are subjected to wear and deterioration in service and if not replaced periodically, ultimate breakage. The prior art revealed in the patent literature disclose braking devices such as the separate safety rail of U.S. Pat. No. 2,084,677 which is engaged at one side by a roller 31 and by a cam 33 which is brought to bear on the safety rail by breakage of a hoisting chain 13. The door is guided in tracks 15 by rollers 14 and the safety rail 30 and the roller 31 and cam 33 function separately from this door guiding function.
Greegor U.S. Pat. No. 2,095,695 also discloses a separate vertical rail apart from the door guiding mechanism which includes flange 4, roller 5 and the flange 9 embraced by the wear plates 6 and 7. The locking rail 23 includes a flange 22 that is adapted to be engaged by a locking bit 19 to prevent the door from falling in the event of failure.
U.S. Pat. No. 2,185,828 to Blodgett provides a safety catch for a vertically acting door that operates in tracks by means of rollers, but utilizes a bottom fixture at each side of the door that incorporates a safety catch, or clutch, which does not rotate during normal operation of the door, but in the event of failure the catch will be engaged within the track in a wedging action to prevent downward movement of the door.
Moler U.S. Pat. No. 2,651,817 describes a safety catch arrangement that involves a dual action having a first frictional wedging engagement and then a piercing engagement if the first engagement slips.
U.S. Pat. No. 3,188,698 to Zoll et al. uses a pawl in the channel shaped guide track having teeth that engage the channel and after initial engagement additional teeth come into operation as the guide channel is dented and expanded by the pawl action.
The overhead door industry has not had a reliable device to prevent such doors from falling in the event of cable breakage. Most such door manufacturers while they have used door stopping devices, the stops were either unreliable or restricted to smaller and lighter weight doors.